1. Field of the Invention
The present invention relates to tire recycling, and more particularly to processing rubber tires into crumb rubber.
2. Description of the Prior Art
The United States alone generates approximately 200,000,000 scrap tires per year. An extremely large percentage of these tires end up in landfills, whereas only a small percentage are recycled.
Efforts have been made to find uses for scrap whole tires to minimize the inundation of scrap tires at landfills. Some of the uses for the scrap whole tires include artificial fishing reefs, oyster beds, floating breakwaters, and impact absorbers around highway and bridge abutments. Whole or cut up portions of scrap tires are also used in playgrounds, flower planters, shoe soles, gaskets, shims, dock bumpers, shock absorbers and floor mats. Whole tires and shredded tire chips may also be burned and used as fuel. Reclaimed rubber is also used in asphalt for roadways.
Notwithstanding the above uses for scrap tires, the plain fact remains that still only a very small percentage of scrap tires end up anywhere but in landfills.
One of the problems associated with reclaiming rubber from scrap tires is that bead wire, steel belts and fiber are embedded in the rubber. Removing the bead wire, steel belts and fiber from the rubber is a costly process, however, reclaimed crumb rubber with the bead wire, steel belts and fiber removed has far many more uses and a value of more than tenfold that of crumb rubber without the bead wire, steel belts and fiber having been removed.
Typically, tires are reclaimed by mechanically grinding the tires into crumb rubber having relatively uniform particle size. Crumb rubber particles passing through a 10-mesh screen or finer are often desired. A 10-mesh screen is one having 10 open spaces per linear inch. Reducing the rubber to this size typically requires several milling steps.
Typically, tires are mechanically ground with a two-roll, grooved rubber mill in which the two mill rolls turn at different rates to provide the shearing action necessary to rip the tire apart. Oftentimes, a tire slitter is used to cut the tire initially. The shredded rubber chunks are screened and the larger chunks are recycled until the desired size is reached. Tire bead wire is removed with magnets or by hand. During intermediate operations, tire fiber is removed with hammermills, reel beaters, and air tables that blow a steady stream of air across the rubber, thus separating the fiber. The separated fiber is blown into collectors and baled. The tire grinding process is very energy intensive.
Cryogenics has also been used in conjunction with mechanical action to make crumb rubber. The rubber is cooled below the glass transition temperature with nitrogen, and the brittle rubber is pulverized in a grinding mill. Whole tires have also been pyrolyzed in a reactor having a tilting grate to discharge the steel belt and bead wire of the tires.
It is desirable to have a dependable, durable and high quality rubber crumbing apparatus which can process shredded steel belted tires into crumb rubber from shredded tire chips. It is also desirable that the rubber crumbing apparatus be capable of producing crumb rubber which will pass through a 10-mesh screen. It is further desirable that the rubber crumbing apparatus be capable of removing steel and fiber from the tire chips to produce a high quality, very usable crumb rubber. It is also desirable that the rubber crumbing apparatus be adjustable to produce various sizes of crumb rubber and be designed to facilitate field maintenance, if required.